HOW DOES THE EYE RESEMBLE THE CAMERA? 151 



smaller amount of light. This change in the size of 

 the pupil is automatic. The eye cannot stand looking 

 into very strong light, nor into a glare, in spite of 

 this adjustment. The iris cannot contract enough to 

 shut out the intense light without also making it 

 difficult to see objects or printed matter. We should 

 therefore avoid straining the eyes by trying to work or 

 read with a bright or glaring light within our field of 

 vision. 



Some Eye Defects. In spite of the wonderful mechan- 

 ism that it is, the eye often has slight defects. The most 



use a Conclave lens to correct. 



1135 



use a convex lews to Correct. fansigktecCness 



common one is astigmatism, due to a slight uneven cur- 

 vature of the lens or the cornea. This difficulty is a fre- 

 quent cause of headaches, and should be attended to by 

 an oculist. 



Another defect is nearsightedness. In this case the 

 eyeball is too long from front to back or the lens too thick, 

 so that the image of distant objects is brought to a focus 

 before reaching the retina. If you have to hold your book 

 close to your eyes, and if you squint when looking at 

 things, you should go to an oculist and have your eyes 

 tested for glasses, as nearsightedness can quickly be cor- 

 rected by this means. 



